Clock controlling method and circuit

ABSTRACT

A clock control circuit comprises a control circuit  102  for outputting a control signal for adding or subtracting a phase to a reference clock, which is an input clock or a clock generated from the input clock, on each clock period of the reference clock, and a phase adjustment circuit  101  fed with the input clock and outputting an output clock having the phase adjusted to the reference clock.

FIELD OF THE INVENTION

[0001] This invention relates to a clock control circuit and a clockcontrol method.

BACKGROUND OF THE INVENTION

[0002] A PLL (phase locked loop) circuit is used in a circuit foradjusting a clock period. FIG. 27 illustrates a conventional PLLcircuit. Referring to FIG. 27, a phase frequency detector (PFD) 319receives an external clock 324 and a signal supplied from a frequencydivider 323 that receives an output of a voltage-controlled oscillator322. A charge pump 320 receives a up signal 325 and a down signal 326both output from a phase frequency detector (PFD) 319 to output avoltage corresponding to a phase difference. A loop filter receives thevoltage from the charging pump 320 to output smoothed voltage which issupplied as a control voltage to the voltage-controlled oscillator (VCO)322. An output clock signal of a, frequency corresponding to the controlvoltage from the voltage-controlled oscillator (VCO) 322 is fed to afrequency divider 323.

[0003] For example, there is proposed in JP Patent Kokai JP-A-11-284497a programmable delay generator in which a ramp waveform voltage fordetermining a delay time and a threshold voltage can be generated bycircuits of the same structure and can be independently set so that itis capable of generating the delay time of a fractional number, anumerator and a denominator of which can be set, a frequency synthesizerwhich, by phase-interpolating output pulses of an accumulator using theprogrammable delay generator, is able to generate an adjustment-freelow-spurious output signal, a multiplication circuit employing theprogrammable delay generator, a duty ratio converter circuit employingthe programmable delay generator as an output pulse width setting delaygenerator, and a PLL frequency synthesizer having the programmable delaygenerator inserted between the frequency divider and a phase comparator.

SUMMARY OF THE DISCLOSURE

[0004] However, the conventional circuit, as shown in FIG. 27, employinga PLL circuit and a feedback type circuit, has drawbacks that phaseadjustment operation is time-consuming and that there exists a jitter(phase noise) proper to a feedback system.

[0005] Moreover, the above-described conventional programmable delaygenerator is in need of a power source voltage generating circuit, suchas a threshold voltage generating circuit, and hence the circuit scaleis increased.

[0006] It is therefore an object of the present invention to provide aclock control circuit and a clock control method whereby non-integerfrequency conversion can be effected with a high degree of accuracy by asimplified configuration.

[0007] For accomplishing the above object, in accordance with one aspectof the present invention is provided a configuration in which a clock isinput and an output clock having a phase difference relative to theinput clock, the phase obtained by adding or subtracting to or from saidphase by a predetermined unit value of a phase differential, on eachconstant period, is output.

[0008] In accordance with another aspect of the present invention, aclock control circuit comprises control means for outputting a controlsignal for adding or subtracting to or from a phase of an output signalrelative to a reference clock which is an input clock or a clockgenerated from the input clock, on each clock period of the referenceclock, and phase adjustment means fed with the input clock forgenerating and outputting output clock having a phase corresponding toaddition or subtraction a preset unit value of a phase differential toor form a phase with respect to the reference clock, based on thecontrol signal, whereby an output clock of a frequency in a non-integerrelation with respect to the frequency of the reference clocks can beoutput.

[0009] In accordance with another aspect of the present invention, isalso provided a clock control circuit comprising a frequency divider foroutputting frequency-divided clock obtained on frequency dividing theinput clock, a control circuit for generating a control signal foradding or subtracting a unit phase difference to or from the input clockwith respect to the frequency-divided clock based on the frequencydivided clock output from the frequency divider and a phase adjustmentcircuit fed with the input clock and generating and outputting an outputclock having a phase prescribed by the control signal from the controlcircuit.

[0010] In accordance with another aspect of the present invention, isprovided a clock control circuit comprising a multi-phase clockgenerating circuit for generating and outputting first to nth clockshaving respective difference phases(multi-phase clocks) from a phase ofthe input clock, a selector fed with the first to nth clocks toselectively output one of the clocks, and a control circuit fed with theinput clock to generate a control signal sequentially selecting thefirst to nth clocks to send the generated selection signal to theselector.

[0011] In accordance with another aspect of the present invention, isprovided a clock control circuit comprising an interpolator receiving afrequency divided signal produced by a frequency dividing circuitreceiving a clock signal and a signal obtained by shifting the frequencydivided signal in a preset number of periods of the clock to produce asignal obtained on division of a timing difference of said two inputsignals at a preset ratio of internal division; and

[0012] a control circuit for varying value of the ratio of the internaldivision of the timing difference in said interpolator based on saidclock signals.

[0013] In accordance with another aspect of the present invention, isprovided a clock control circuit comprising a plurality of (N)interpolators for outputting signals obtained on dividing a timingdifference of two input signals with respective different values of apreset ratio of internal division; wherein of first to nth clocks withrespective different phases, two clocks, that is the Ith and the (I+1)stclocks, where I is an integer from 1 to N, with N+1 being 1, are inputto the Ith interpolator.

[0014] In accordance with another aspect of the present invention, theinterpolator comprises a logic circuit fed with first and second inputsignals to output a result of preset logical processing of said firstand second input signals;

[0015] a first switching device connected across a first power sourceand an internal node, said first switching device being fed at a controlterminal thereof with an output signal of said logic circuit and beingsturned on when said first and second input signals are both of a firstvalue;

[0016] a buffer circuit having an input terminal connected to saidinternal node and having an output logical value changed on inversion ofrelative magnitudes of the terminal voltage of the capacitance of saidinternal node and a threshold value;

[0017] a plurality of serial circuits connected across said internalnode and a second power source in parallel, each of said serial circuitsbeing made up of a second switching device turned on when said firstinput signal is of a second value, said third switch device turned on oroff based on a control signal from said control circuit, and a firstconstant current source; and

[0018] a plurality of serial circuits connected across said internalnode and a second power source in parallel, each of said serial circuitsbeing made up of a fourth switching device turned on in common when saidfirst input signal is of a second value, said fifth switching deviceturned on or off based on a control signal from said control circuit,and a constant current source.

[0019] In accordance with another aspect of the present invention, saidinterpolator comprises a logic circuit receiving first and second inputsignals to output results of preset logical processing of said first andsecond input signals;

[0020] a first switching device connected across a first power sourceand an internal node, said first switching device being fed at a controlterminal thereof with an output signal of said logic circuit and beingturned on when said first and second input signals are both of a firstvalue; and

[0021] a buffer circuit having an input end connected to said internalnode and having an output logical value changed on inversion of therelative magnitudes of the terminal voltage of the capacitance of saidinternal node and a threshold value;

[0022] a plurality of serial circuits connected across said internalnode and a second power source in parallel, each of said serial circuitsbeing made up of a second switching device turned on when said firstinput signal is of a second value, said third switch device turned on oroff based on a control signal from said control circuit, and a firstconstant current source;

[0023] a plurality of serial circuits connected across said internalnode and a second power source in parallel, each of said serial circuitsbeing made up of a fourth switching device turned on in common when saidfirst input signal is of a second value, said fifth switching deviceturned on or off based on a control signal from said control circuit,and a constant current source; and

[0024] a plurality of serial circuits connected across said internalnode and the second power source in parallel, each said serial circuitbeing made up of a sixth switching device and a capacitor device; thevalue of said capacitance attached to said internal node beingdetermined by a period control signal supplied to a control terminal ofsaid sixth switching device.

[0025] In accordance with another aspect of the present invention, aclock control method comprises the steps of generating an output clockhaving a phase relative to a reference clock by adding or subtracting toor from said phase by a predetermined unit value of a phase differentialon each clock period of said reference clock, said reference clock beingan input clock or a clock derived from the input clock; and outputtingsaid output clock.

[0026] Still other objects and advantages of the present invention willbecome readily apparent to those skilled in this art from the followingdetailed description, wherein only the preferred embodiment of theinvention is shown and described, simply by way of illustration of thebest mode contemplated of carrying out this invention. As will berealized, the invention is capable of other and different embodiments,and its several details are capable of modifications in various obviousrespects, all without departing from the invention. Accordingly, thedrawing and description are to be regarded as illustrative in nature,and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 shows a configuration of a first embodiment of the presentinvention.

[0028]FIG. 2 is a timing chart for illustrating operation of the firstembodiment of the present invention.

[0029]FIG. 3 shows a configuration of a second embodiment of the presentinvention:

[0030]FIG. 4 shows a configuration of a third embodiment of the presentinvention.

[0031]FIG. 5 shows an illustrative structure of a multi-phase clockgenerating circuit of a third embodiment of the present invention.

[0032]FIG. 6 shows an illustrative structure of the four-phase clockgenerating circuit of the third embodiment of the present invention.

[0033]FIG. 7 is a timing diagram for illustrating the operation of thefour-phase clock generating circuit of the third embodiment of thepresent invention.

[0034]FIG. 8 shows an illustrative structure of a circuit configurationof a timing difference division circuit (interpolator) of FIG. 6.

[0035]FIG. 9 is a timing diagram for illustrating the operation of atiming difference division circuit (interpolator) of FIG. 6.

[0036]FIG. 10 shows a modification of a timing difference divisioncircuit (interpolator).

[0037]FIG. 11 illustrates an operating principle of the timingdifference division circuit (interpolator).

[0038]FIG. 12 shows a first embodiment of the circuit configuration of avariable internal division ratio interpolator used in an embodiment ofthe present invention.

[0039]FIG. 13 shows a second embodiment of the circuit configuration ofa variable internal division ratio interpolator used in an embodiment orthe present invention.

[0040]FIG. 14 shows a third embodiment of the circuit configuration of avariable internal division ratio interpolator used in an embodiment ofthe present invention.

[0041]FIG. 15 shows a fourth embodiment of the circuit configuration ofa variable internal division ratio interpolator used in an embodiment ofthe present invention.

[0042]FIG. 16 shows the configuration of a fourth embodiment of thepresent invention.

[0043]FIG. 17 is a timing chart for illustrating the operation of thefourth embodiment of the present invention.

[0044]FIG. 18 shows the configuration of a fifth embodiment of thepresent invention.

[0045]FIG. 19 is a timing chart for illustrating the operation of thefifth embodiment of the present invention.

[0046]FIG. 20 shows the configuration of a sixth embodiment of thepresent invention.

[0047]FIG. 21 is a timing chart for illustrating the operation of thesixth embodiment of the present invention.

[0048]FIG. 22 shows a configuration of a seventh embodiment of thepresent invention.

[0049]FIG. 23 shows a configuration of an eighth embodiment of thepresent invention.

[0050]FIG. 24 shows a configuration of a ninth embodiment of the presentinvention.

[0051]FIG. 25 shows a layout of a 16-equi-division interpolator used inthe embodiments of the present invention.

[0052]FIG. 26 is a waveform diagram showing the results of simulation ofthe output of the phase adjustment circuit employing theq6-equi-division interpolator in the embodiments of the presentinvention.

[0053]FIG. 27 shows a typical conventional clock control circuit.

PREFERRED EMBODIMENTS OF THE INVENTION

[0054] Preferred embodiments of the present invention are described inthe bellow. In a preferred embodiment of the present invention, a clockcontrol circuit comprises a control circuit (102 of FIG. 1) foroutputting a selection control signal for selecting incrementing(adding) or decrementing (Subtracting) to or from a phase relative to areference clock, by a predetermined unit value of a phase differentialon each reference clock cycle, which is an input clock or a clockgenerated from an input clock; and a phase adjustment circuit (101 ofFIG. 1) fed with the input clock and generating an output clock having aphase corresponding to incrementing or decrementing a predetermined unitphase value of a phase differential with respect to the reference clock,based on the control signal, whereby an output clock of a frequency in anon-integer relation with respect to the frequency of the referenceclock can be output.

[0055] In another preferred embodiment of the present invention, a clockcomprises a frequency divider (103 of FIG. 3) for outputtingfrequency-divided clocks obtained by frequency dividing the input clock,a control circuit (102 of FIG. 3) for generating a control signal foradding or subtracting to or from a phase by a unit phase differentialrelative to the input clock with respect to the frequency-divided clocksbased on the frequency divided clocks output from the frequency divider,and a phase adjustment circuit (101 of FIG. 3) fed with the input clockand generating and outputting an Output clock having a phase prescribedby the control signal from the control circuit.

[0056] In another preferred embodiment of the present invention, a clockcontrol circuit comprises a multi-phase clock generating circuit (201 ofFIG. 4) for generating and outputting first to nth clocks havingrespective difference phases from the phase of the input clock(multi-phase clocks), and a selector (203 of FIG. 4) fed with the firstto nth clocks to selectively output one of the clocks and a controlcircuit (202 of FIG. 4) fed with the input clock to generate a controlsignal sequentially selecting the first to nth clocks to send thegenerated selection signal to the selector.

[0057] According to the present invention, the phase adjustment circuitis comprises an interpolator for dividing timing difference of two inputsignals to output a signal. There is provided a control circuitoperating so that a signal obtained on frequency division of the clocksignals and a signal shifted preset clock periods are input to theinterpolator and the timing difference division ratio in theinterpolator is changed based oil the clock signals.

[0058] Alternatively, there may be provided plural interpolators, eachof which outputs a signal, a propagation delay of said signalcorresponding, to the division of timing difference between two inputsignals. The values of timing difference division ratio in the pluralinterpolators are set to respective different values. Plural sets of twoclocks of plural (N) clocks of different phase may be input to theplural interpolators so that both end side clocks, that is the first andNth clocks are provided to one interpolator.

[0059] In another preferred embodiment of the present invention, a clockcontrol circuit comprises a multi-phase multiplication clock generatingcircuit (10 of FIG. 20) for generating first to nth clocks, phases ofwhich are different (termed multi-phase multiplication clocks) obtainedon multiplying input clock based on the input clock,

[0060] a switch (20 of FIG. 20 for selecting two of the first to nthclocks output from the multi-phase multiplication clock generatingcircuit,

[0061] an interpolator (30 of FIG. 20) fed with the two clock signalsselected and output by the switch to output a signal corresponding todivision of the two clock signals, with a ratio of the internal divisionbeing variably set, and

[0062] a control circuit (40 of FIG. 20) for outputting a switchingsignal for the switch and a control signal for variably setting theratio of the internal division of the timing difference of theinterpolator.

[0063] In another preferred embodiment of the present invention, a clockcontrol circuit comprises a multi-phase multiplication clock generatingcircuit (10 of FIG. 22) for generating first to nth clocks of respectivedifferent phases(multi-phase multiplication clocks) obtained onmultiplying frequency divided input clock based on the input clock,

[0064] a switch (20 of FIG. 22) for selecting two sets each of twoneighboring ones of the first to nth clocks output from the multi-phasemultiplication clock generating circuit,

[0065] a first interpolator (30 ₁ of FIG. 22) fed with the first set oftwo clocks output from the switch to output a signal, a propagationdelay of said signal corresponding to division of the timing differenceof the two clock signals,

[0066] a second interpolator (30 ₂ of FIG. 22) fed with the second setof two clocks output from the switch to output a signal, a propagationdelay of said signal corresponding to division of the timing differenceof the two clock signals,

[0067] a third interpolator (30 ₃ of FIG. 22) fed with outputs of thefirst and second interpolators to output a signal, a propagation delayof said signal corresponding to division of the timing difference of thetwo outputs, and

[0068] a control circuit (40 of FIG. 22) for outputting a switchingsignal for the switch and a control signal for variably setting ratio ofthe internal division of the timing difference of the interpolators. Theratio of the internal division of the timing difference of at least oneof the first to third interpolators can be set variably.

[0069] The multi-phase multiplication circuit comprises a frequencydivider (2 of FIG. 5) for frequency dividing an input clock to generateand output a plurality of clocks of different phases (multi-phaseclocks). a period detection circuit (6 of FIG. 5) for detecting a periodof the input clock and a multi-phase clock multiplication circuit (5 ofFIG. 5) fed with the multi-phase clocks corresponding to frequencymultiplied clocks in generate multi-phase clocks corresponding tomultiplication of the clocks.

[0070] The multi-phase clock multiplication circuit preferably comprisesa plurality of timing difference division circuits (4 a 1 to 4 a 8 ofFIG. 6) for outputting a signal corresponding to the division of thetiming difference of two inputs and a plurality of multiplexing circuits(4 b 1 to 4 b 4 of FIG. 6) multiplexing two outputs of the timingdifference division circuits to Output the resulting multiplexedsignals.

[0071] The timing difference division circuit include timing differencedivision circuits (4 a 1, 4 a 3, 4 a 5, 4 a 7 of FIG. 6) fed with clocksof the same phase and timing difference division circuits (4 a 2, 4 a 4,4 a 6, 4 a 8 of FIG. 6) fed with two clocks of neighboring phases.

[0072] The multi-phase clock multiplication circuits (5) preferablycomprises 2n timing difference division circuits for outputting signalscorresponding to division of the timing difference of two inputs,wherein

[0073] (2I−1)st timing difference division circuits (4 a 1 to 4 a 8 ofFIG. 6), where 1≦I≦n, are fed with the same Ith clocks as the twoinputs,

[0074]2Ith timing difference division circuits (4 a 2, 4 a 4, 4 a 6, 4 a8 of FIG. 6), where 1≦I≦n, are fed with the Ith clocks and with the (I+1mod n)th clocks, where mod denotes remainder calculations and I+1 mod nmeans the remainder of the division of (I+1) with m,

[0075]2n pulse width correction circuits (4 c 1 to 4 c 8 of FIG. 6) fedwith outputs of Jth timing difference division circuits, where 1≦J≦2n,and with outputs of (J+2 mod n)th timing difference division circuits,where J+2 mod n means the remainder of division of J+2 with n, and

[0076] n multiplexing circuits (4 b 1 to 4 b 4 of FIG. 6) fed withoutputs of Kth pulse width correction circuit, where 1≦K≦n, and withoutputs of the (K+n)th pulse width correction circuits.

[0077] In another preferred embodiment of the present invention, a clockcontrol circuit comprises a frequency divider (60 of FIG. 23) fed withinput clock to generate two sets of clocks of respective differentphases obtained on frequency division of the input clock,

[0078] a first interpolator (30 ₁ of FIG. 23) fed with the first set oftwo clocks output from the frequency divider to output a signal, apropagation delay of said output signal corresponding to division oftiming difference of the two clock signals,

[0079] a second interpolator (30 ₂ of FIG. 23) fed with the second setof two clocks output from the frequency divider to output a signal, apropagation delay of said output signal corresponding to division oftiming difference of the two clock signals,

[0080] a third interpolator (30 ₃ of FIG. 23) fed with outputs of thefirst and second interpolators to output a signal, a propagation delayof said output signal corresponding to division of timing difference ofthe two outputs, with the ratio of the internal division of the timingdifference of at least one of the first to third interpolators beingvariably set, and

[0081] a control circuit (40 of FIG. 23) for outputting a switchingsignal for the switch and a control signal for variably setting theratio of the internal division of the timing difference of theinterpolators.

[0082] In another preferred embodiment of the present invention, a clockcontrol circuit comprises a multi-phase multiplication clock generatingcircuit (10 of FIG. 24) for generating plural clocks of respectivedifferent phases obtained on frequency multiplying input clock based onthe input clock,

[0083] a plurality of interpolators (30 _(l) to 30 _(n) of FIG. 24) fedwith two clocks of neighboring phases of the plural clocks output fromthe multi-phase multiplication clock generating circuit to outputsignals, propagation delay of said signals corresponding to divisionwith respective different values of ratio of internal division of timingdifference of the two clocks and

[0084] a synthesis unit (50 of FIG. 24) fed with outputs of the pluralinterpolators to multiplex the outputs of the interpolators to output aresulting sole output signal.

[0085] In this embodiment, the multi-phase multiplication clockgenerating circuit generates N phase clocks, where N is a presetpositive integer, M of the interpolators are provided, where M is apositive integer such that M≦N.

[0086] The ith interpolator is fed with ith and (i+1)st clocks, where iis an integer from 1 to M while the (n+1)st clock is treated as a firstclock. A value of ratio of internal division dividing timing differenceof two input signals in each of the interpolators is so set that theratio value of the (i+1)st interpolator is larger or smaller than thatof the ith interpolator by a preset unit step.

[0087] M-phase clocks are output from the M interpolators and whereinM-tupled clocks are output from the synthesis unit. The internaldivision ratio dividing the timing different of the two interpolators isof a fixed value.

[0088] In the above-described embodiment of the present invention, shownin FIGS. 12 to 15, the interpolator comprises

[0089] a logic circuit (NAND01) fed with first and second input signalsto output results of preset logical processing of the first and secondinput signals,

[0090] a first switching device (MP1) connected across a first powersource and an internal node (N31), the first switching device being fedat a control terminal thereof with an output signal of the logic circuitand being turned on when the first and second input signals are both ofa first value,

[0091] a buffer circuit (INV3) having an input end connected to theinternal node and having an output logical value changed on inversion ofthe relative magnitudes of the terminal voltage of the capacitance ofthe internal node and a threshold value,

[0092] a plurality of serial circuits connected across the internal nodeand a second power source in parallel, each of the serial circuits beingmade up of a second switching device (MN11) turned on when the firstinput signal (IN1)is of a second value, the third switch device (MN21)turned on or off based on a control signal (PH) from the control circuit(40 of FIG. 20), and a constant current source (I₀),

[0093] a plurality of serial(series) circuits connected across theinternal node and a second power source in parallel, each of the serialcircuits being made up of a fourth switching device (MN12) turned on incommon when the first input signal is of a second value, the fifthswitching device (MN22) turned on or off based on a control signal fromthe control circuit, and a constant current source (I₀).

[0094] The third switching device (MN21) may be connected on the site ofthe internal node (N31),with the second switching device (MN11) thenbeing connected to the side of the constant current source (I₀) in aninterchanging fashion. The fourth switching device (MN12) may, ofcourse, be interchanged with the fifth switching device (MN22).

[0095] A plurality of serial circuits, each made up of a sixth switchingdevice and a capacitor (MN31 to MN34 and CAP11 to CAP 14), arc connectedin parallel across the internal node (N31) and the second power source.The value of capacitance to be attached to the internal node isselectively determined by the periodic control signal 7 supplied to thecontrol terminal of the group of the sixth switching devices (MN31 toMN34).

[0096] For more detailed explanation of a preferred embodiment of thepresent invention, certain preferred embodiments of the presentinvention will be explained with reference to the drawings.

[0097]FIG. 1 illustrates a structure of a first embodiment of thepresent invention. Referring to FIG. 1, the first embodiment of thepresent invention comprises a phase adjustment circuit 101 that receivesan input clock and generate an output clock having a phase adjusted withrespect to a reference clock as which is used the input clock or asignal derived from the input clock and a control circuit 102 thatreceives the input clock and the code information to output a selectionsignal to the phase adjustment circuit 101.

[0098] Preferably, the phase adjustment circuit 101 comprises ,ininterpolator in which a interior division ratio of timing difference isvariably set in a programmable way.

[0099] The control circuit 102 comprises an addition circuit forincrementing a preset unit m (m=1, 2, 3, . . . ) from an initial value 0(0, m, 2m, 3m, . . . ) each time it is fed with the input clock. Thepreset value m is set by a code signal input to the control circuit 102from outside.

[0100] The control circuit 102 may comprises a subtraction circuit fordecrementing a preset unit m (m=1, 2, 3, . . . ) e.g., from the initialvalue N each time it is fed with an input clock. A result of thesubtraction is decoded and a selection signal (control signal)corresponding to the result of the subtraction is supplied to the phaseadjustment circuit 101. The value of the preset unit m is set by a codesignal input from outside to the control circuit 102.

[0101] Based on the selection signal from the control circuit 102, thephase adjustment circuit 101 outputs a signal comprising pulse edgeswith phase differences of 0, ΔΦ, 2 ΔΦ, 3ΔΦ, . . . , (n−1)ΔΦ, n, . . . ,from corresponding edges, such as rising edges of an input clock with aperiod tCK, where ΔΦ is a unit phase differential which is determined bythe selection signal from the control circuit 102. It is noted that nΔΦis equivalent to phase difference 0.

[0102] With the unit phase difference ΔΦ, for the selection signal “m”from the control circuit 102 being “1”, the unit phase difference in thephase adjustment circuit 101 is mΔΦ, such that signal with phasedifferences of 0, mΔΦ, 2m ΔΦ, 3m ΔΦ, . . . , (n−1)mΔΦ, nmΔΦ, . . . isoutput from one input clock to another. It is noted that, with the unitphase difference ΔΦ of tCK/n, nmΔΦ is equivalent to the phase difference0.

[0103] Referring to FIG. 2, showing the operating principle of the firstembodiment of the present invention, a phase difference of an outputclock relative to a rising edge of an input clock in a clock cycle 1 is0,

[0104] a phase difference of the output clock relative to a rising edgeof the input clock in a clock cycle 2 is ΔΦ and

[0105] a phase difference of the output clock relative to a rising edgeof the input clock in a clock cycle 3 is 2ΔΦ, and so on.

[0106] A period of the output clock is tCK +ΔΦ, such that a frequencyf=1tCK of the input clock hiving a clock period tCK isfrequency-converted into a frequency=1/(tCK +ΔΦ). A clock period isfrequency-converted with a value other than integer ratio(non-integervalue) (=1+ΔΦ/tCK) of the input clock frequency.

[0107] When the output clock and the input clock are interchanged inFIG. 2, the result is the timing operation of the control circuit 102made up of a subtraction unit and a decoder. If the control circuit 102comprises a subtraction unit, the phase differences of the output clockrelative to the rising edge of the input clock is—ΔΦ, −2ΔΦ, . . . .

[0108] A second embodiment of the present invention is now explained.FIG. 3 illustrates a structure of the second embodiment of the presentinvention. Referring to FIG. 3, the second embodiment includes afrequency divider 103 for frequency dividing input clock, a controlcircuit 102 and a phase adjustment circuit 101. The frequency divider103 is fed with an input clock to frequency divide the input clock foroutputting a frequency divided clock.

[0109] The control circuit 102 comprises an adder for incrementing codesignals m (m=1, 2, 3, . . . ) from an initial value 0 to (0, 2m, 3m, . .. ) each time it is fed with the input clock, and a decoder for decodingthe output of the adder to output a selection signal associated with thedecoded value to the phase adjustment circuit 101.

[0110] With a unit phase difference of ΔΦ, the phase adjustment circuit101 outputs a signal comprising pulse edges with phase differences of 0.mΔΦ, 2mΔΦ, 3mΔΦ, . . . , (n−1)mΔΦ, nmΔΦ, . . . , from correspondingedges of the input clock, based on the selection signal from the controlcircuit 102, from one input clock to another. It is noted that, with theunit phase difference ΔΦ equal to tCK/n, nmΔΦ is equivalent to phasedifference 0.

[0111] A frequency f=b 1/tCK of the input clock with a period of tCK isconverted into a frequency=1/(tCK +ΔΦ), with the period of the outputclock being tCK +ΔΦ, such that the clock period can be changed to avalue other than an integer ratio.

[0112] In the present second embodiment, the control circuit 102 may, ofcourse, be made Up of a subtraction unit and a decoder.

[0113] A third embodiment of the present invention is now explained.FIG. 4 illustrates a structure of the third embodiment of the presentinvention. Referring to FIG. 4, the present third embodiment includes amulti-phase clock generator 201, a selector 202 and a control circuit203 for supplying a selection signal to the selector 202.

[0114] The multi-phase clock generator 201 output n th clocks, a timing(phase) difference between clocks with neighboring phases clocks isΔΦ=tCK/n.

[0115] The first to the nth clocks are selected in a cyclic way by theselector 202, under control by the control circuit 203, such that

[0116] the first clock is selected in a clock cycle 1, with the phasedifference of the output clock relative to the rising edge of the inputclock being 0;

[0117] the second clock is selected in a clock cycle 2, with the phasedifference of the output clock relative to the rising edge of the inputclock being ΔΦ; and

[0118] the third clock is selected in a clock cycle 3, with the phasedifference of the output clock relative to the rising edge of the inputclock being 2ΔΦ, and so on.

[0119] The period of the output clock is tCK +ΔΦ, such that thefrequency f=1/tCK of the input clock with the period tCK is converted tothe frequency=(tCK+ΔΦ), to render it possible to convert the clockperiod with a value other than an integer (=1+ΔΦ/tCK).

[0120] The above-described embodiment of the present invention will beexplained in further detail. In the following, the present embodiment isexplained in detail based on the circuit structure shown in FIG. 4, inconsideration of a sequence of explanation of the timing differencecircuit (interpolator) characteristic of the present invention.

[0121]FIG. 5 illustrates an example of a structure of the multi-phaseclock generator 201 shown in FIG. 4. FIG. 6 shows a specified embodimentof the structure of a multiplication interpolator embodying the presentinvention as a multi-phase clock generator 201 generating four-phaseclocks.

[0122] Referring to FIG. 5, the four-phase clock generator includes a ¼frequency divider 2 for frequency-dividing an input clock 1 by four tooutput four-phase clocks Q1 to Q4, a n-stage cascade-connectedfour-phase clock multiplication circuits(termed frequency doublingcircuits) 51 to 5n and a period detection circuit 6. Meanwhile, thenumber of the stages n of the four-phase clock multiplication circuitsis arbitrary

[0123] The ¼ frequency divider 2 divides a frequency of the input clockby ¼ to generate four-phase clocks Q1 to Q4, which then are multipliedby the four-phase clock multiplication circuit 51 to generate four-phaseclocks Q11 to Q14. Similarly, four-phase clocks Qn1 to Qn4 are obtainedby the four-phase clock multiplication circuit 5n by 2n frequencymultiplication.

[0124] The period detection circuit 6 is made up of a fixed number ofstages of ring oscillators and a counter, both bot shown. During oneclock period, the number of oscillations of the ring oscillator iscounted by the counter and a control signal 7 corresponding to thenumber of counts is output to adjust a load in the four-phase clockmultiplication circuit 5. This period detection circuit 6 operates toeliminate fluctuations in device characteristics and in the operatingrange of the clock period.

[0125]FIG. 6a illustrates a structure of the four-phase clockmultiplication circuit 5 shown in FIG. 5. Meanwhile, the four-phaseclock multiplication circuits 51 to 5n shown in FIG. 5 are of the samestructure. Referring to FIG. 6a, this four-phase clock multiplicationcircuit 5 is made up of eight timing difference division circuits 4 a 1to 4 a 8, eight pulse width correction circuits 4 cl to 4 c 8 and fourmultiplexing circuits 4 b 1 to 4 b 4. FIG. 6b shows a structure of apulse width correction circuit 4 c, comprised of a NAND circuit 16 fedwith a signal corresponding to a second input complemented by theinverter 17 and with a first input. FIG. 6c shows a structure of themultiplexing circuit 4 b comprised of a two-input NAND circuit 18.

[0126]FIG. 7 illustrates signal waveforms diagram for explainingoperational timing of the four-phase clock multiplication circuit 5shown in FIG. 6. A rise timing of the clock T21 is determined by aninternal delay of the timing difference division circuit 4 al from arising edge of the clock Q(n−1)1, whilst a rise timing the clock T22 isdetermined by a timing division of a difference between a rise timing ofthe clock Q(n−1) and a rise timing of the clock Q(n−1) 2, and aninternal delay of in the timing difference division circuit 4 a 2.

[0127] Similarly, rise timing of the clock T26 is determined by a timingdivision of a difference between a rise timing of the clock Q(n−1) 3 anda rise timing of the clock Q(n−1) 4 and the internal delay in the timingdifference division circuit 4 a 2,

[0128] a rise timing of the clock T27 is determined by the internaldelay of a rise timing of the clock Q(n−1) 2 in the timing differencedivision circuit 4 a 7 and

[0129] a rising edge of the clock T28 is determined by a timing divisionof a difference between a rise timing of the clock Q(n−1) 4 and a risetiming of the clock Q(n−1) 1 and the internal delay in the timingdifference division circuit 4 a 8.

[0130] The clocks T21 and T23 are fed to the pulse width correctioncircuit 4 cl which then outputs a pulse P21 having a falling edgedetermined by the clock T21 and a pulse P21 having a rising edgedetermined by the clock T23. By a similar sequence of operations, pulsesP22 to P28 are generated, with the clocks P21 to P28 being duty 25%eight-phase pulses evenly spaced by phase 45. The clock P25, spaced by180° from the clock P21, is multiplexed and inverted by the multiplexingcircuit 4 b 1 and output as a duty 25% clock Qn1.

[0131] In similar manner, clocks Qn2 to QN4 are generated. The clocksQn1 to QN4 become duty 50% four-phase pulses, equally-spaced by 90°. Theclocks Qn1 to QN4 are frequency multiplied by a factor of two in thecourse of generating the clocks Qn1 to Qn4 from the Q(n−1)1 to Q(n−)4.

[0132]FIG. 8a and FIG. 8b illustrate typical structures of the timingdifference division circuits 4 al and 4 a 2, respectively, shown in FIG.7. These circuits are of the same structure and differ as to whether thetwo inputs are the same signal or two neighboring signals are input.That is, the timing difference division circuits 4 al and 4 a 2 are thesame, in structure except that the same input Q(n−1)1 is input to atwo-input NOR 51 in the timing difference division circuit 4 al whereasQ(n−0)1 and Q(n−1)2 are input to the two-input NOR 61. The two-inputNORs 51, and 61 are comprised of two P-channel MOS transistors connectedin series across the power source VDD and an output end and areconnected in parallel across and to the gate of which input signals IN1,IN2 are fed, and two N-channel MOS transistors connected in parallelacross an output terminal and the ground and to the gates of which arefed input signals IN1, IN2.

[0133] An internal node N51 (N61) as an output node of the two-input NOR51 (NOR 61) is connected to an input terminal of an inverter INV51(INV61). Across the internal node and the ground are connected, inparallel, a circuit comprised of a serial connection of a N-channel MOStransistor MN 51 and a capacitor CAP 51, a circuit comprised of a serialconnection of a N-channel MOS transistor MN 52 and a capacitor CAP 52and a circuit comprised of a serial connection of a N-channel MOStransistor MN53 and a capacitor CAP 53. The gates of the respective MOStransistors MN51 to MN53 are fed with control signals 7 from the perioddetection circuit 6 so as to be thereby turned on or off. The gatewidths of the MOS transistors MN51 to MN53 and the capacitors CAP 51 toCAP 53 are controlled to a size ratio of for example, 1:2:4, with theclock period being set by adjusting the load connected to the commonnode in eight stages based on the control signal 7 output from theperiod detection circuit 6 (see FIG. 5).

[0134]FIG. 9 shows a timing diagram for explaining the operation of thetiming difference division circuits 4 al and 4 a 2.

[0135] As for the timing difference division circuit 4 al, electricalcharge of the node N51 is extracted through an N-channel MOS transistorof the NOR 51 and, as a potential of the node N51 has reached athreshold Value of the inverter N51, the clock T21 as an output of theinverter INV51 rises.

[0136] Assuming that a value of the electrical charge of the node N51,that need to be extracted when the threshold value of the inverter INV51 is reached, is CV, where C and V denote capacitance and voltage,respectively, and a discharge current by the N-channel MOS transistor ofNOR 51 is I, the electrical charge CV is discharged with a current value2I as from the rising of the clock Q(n−1)1.

[0137] So, the time CV/21 denotes a timing difference (propagation delaytime) as from the rising edge of the clock Q(n−1) until the rising ofthe clock T21. With the clock Q(n−11) at Low level(logic low), theoutput side node N51 of the two-output NOR 51 is charged to Highlevel(logic high), with the output clock of the inverter INV 51 falls toLow level.

[0138] As for the timing difference division circuit 4 a 2, theelectrical charge at the node N61 are extracted to NOR 61 during thetime as from a rising edge of the clock Q(n−1)1 until time tCKn(tCKn=clock period). When a potential of the node N61 has reached athreshold value of the inverter INV 61, as from a rising edge of theQ(n−1)2, the edge of the clock T22 rises.

[0139] If the electrical charge of the node N61 is CV and a dischargecurrent of the NMOS transistor of the two-input NOR 61 is I, and theelectrical charge CV is extracted from a rising edge of the clockQ(n−1)1 with the current I during time of tCKn, and with the current 2Ifor the remaining time, the time

tCKn+(CV−tCKn·I)/2I

=CV/2I +tCKn/2  (1)

[0140] denotes the timing difference as from the rising edge of theclock Q(n−1) until the rising edge of the clock T22.

[0141] That is, a difference of rise timings between clocks T22 and T21is tCKn/2.

[0142] If both the clock Q(n−1)1 and Q(n−1)2 are at Low level and theoutput side node N61 of the two-input NOR 61 is charged to High levelfrom the power source through the PMOS transistor of NOR 61, the clockT22 rises.

[0143] The same holds for the clocks T22 to T28, with the rising timingsdifference of the clocks T21 to t28 being each tCKn/2

[0144] The pulse correction circuits 4 cl to 4 c 8 (FIG. 6) generateduty 25% eight-phase pulses P21 to P28, dephased each 45° (see FIG. 7).

[0145] The multiplexing circuits 4 b 1 to 4 b 4 (see FIG. 6) generateduty 50% four-phase pulses Qn1 to Qn4, dephased each by 90°, as shown inFIG. 7

[0146] If clocks Qn1 to Qn4 of FIG. 7 are output from the four-phaseclock generator 201, the selector 203, fed with Qn1 to Qn4, sequentiallyselects and outputs the clocks Qn1 to Qn4, in a sequence of the Qn1,Qn2, Qn3 and Qn4 under control by a selection signal from the controlcircuit 202. With a period T of the clocks being Qn1 to Qn4, clock witha period of T(1+¼) are output from the selector 203.

[0147]FIG. 10 shows another embodiment of the timing difference divisioncircuit used in the four-phase clock multiplication circuit shown inFIG. 6 etc. Referring to FIG. 10, in the timing difference divisioncircuit, a logical OR circuit OR1 receives a first and second inputsignals IN1, IN2.

[0148] A P-channel MOS transistor MP1 is connected across the powersource VCC and an internal node N26 and a gate of MOS transistor MP1 isfed with an output signal of the logical OR circuit OR1

[0149] An inverter INV3 has its input terminal connected to the internalnode N26 for inverting and outputting a potential of the internal nodeN26.

[0150] N-channel MOS transistors MN1, MN2, have drains, gates andsources connected to the internal node N26, fed with the first andsecond input signals IN1, IN2 and connected to a constant current sourceI₀, respectively.

[0151] Across the internal node N26 and the ground are connectedswitching devices MN11 to MN15, comprised of N-channel MOS transistors,and the capacitors CAP 11 to CAP 15.

[0152] To control terminals, (gate terminals) of the switching devicesMN11 to MN15, comprised of N-channel MOS transistors, are coupledcontrol signals 7 output from the period detection circuit 6 of FIG. 5,as in the case of the timing difference division circuits explained withreference to FIG. 8.

[0153] The switching devices MN11 to MN15 are controlled on or offdepending on value of the control signal 7 to decide capacitance valueto be attached to the internal node N26.

[0154] The capacitance ratio of the capacitors CAP 11 to CAP15 is set tosuch as 16:8:4:2:1, with the ratios of the gate widths (W) to the gatelengths (L) of the N-channel MOS transistors MN11 to MN15 being16:8:4:2:1.

[0155] If the first and second input signals IN1, IN2 are at Low level,in output of the OR circuit OR1 is low, such that the P channel MOStransistor MP1 is turned on to charge the internal node N26 to the powersource potential, with the output of the inverter INV3 then being at Lowlevel.

[0156] If one or both of the first and second input signals IN1, 1N2 isor are at High level, an output of the logical OR circuit OR1 changes toHigh level, and the P-channel MOS transistor MP1 is tuned off, so thatthe power source path of the power source Vcc and the internal node N26is turned OFF.

[0157] On the other hand, one or both of the N-channel MOS transistorsMN1 and MN2 are turned ON to discharge the internal node N26 so that thepotential of the internal node N26 starts to be decreased from the powersource potential. When the potential of the internal node N26 falls tobelow the threshold voltage of the inverter INV3, an output of theinverter INV3 rises from Low level to High level.

[0158]FIG. 11 illustrates operation of the timing difference divisioncircuit TMD shown in FIGS. 8 and 10. Referring to FIG. 11a, first one ofthree timing difference division circuits (TMD) is fed at its two inputswith the same input signal IN1 to output an output signal OUT1, whilesecond timing difference division circuit (TMD) is fed at its two inputswith input signals IN1 and IN2 to output an output signal OUT2 and thirdtiming difference division circuits (TMD) is fed at its two inputs withthe same input signal IN2 to output an output signal OUT3.

[0159] Of these, the second timing difference division circuit (TMD),fed with the input signals IN1, IN2 to output the output signal OUT2,corresponds to the structure of the timing difference division circuitof FIG. 8b.

[0160] The timing difference division circuit (TMD) fed with IN1 incommon and the timing difference division circuit (TMD) fed with IN2 incommon are fed with the same signal in FIG. 8a and corresponds to thestructure of the timing difference division circuit 4 a 2 of FIG. 8a.

[0161]FIG. 11b shows output signals OUT1 to OUT3 of the first to thirdtiming difference division circuits, fed with the input signals IN1, IN2of the timing difference T, and changes A1 to A3 of the internal nodesof the first to third timing difference division circuits.

[0162] For ease of understanding, it is assumed that the internal nodeis charged from an electrical potential 0 and that the output signal ischanged from low to High level when the threshold value Vt is exceeded.

[0163] Referring to FIG. 11b, there is timing difference between theinput signals IN1 and IN2, the first timing difference division circuitTMD outputs an output signal OUT1 with a delay time(propagation delay)t1, the third timing difference division circuit TMD outputs an outputsignal OUT3 with a delay time t3 and the second timing differencedivision circuit TMD outputs an output signal OUT2 with a delay time t2,with the delay time t2 being a value corresponding to internal divisionof the delay time t1 and the delay time t3.

[0164] Meanwhile,

t1CV/2I,

t2=T+(CV−IT)/(2I)

-−T/2+CV/2I  (2).

[0165] On the other hand, T+CV/21 (see FIG. 11c), provided thatelectrical charge discharged until the threshold value of a buffercircuit (inverter) to which is connected the inner node are denoted CV.

[0166] The structure of an interpolator, used in e.g., the phaseadjustment circuit 101 in the embodiment of the present invention and inwhich the ratio of internal division of the timing differences of thetwo input signals can be variably set, is explained.

[0167]FIG. 12 illustrates a structure of an interpolator forming thephase adjustment circuit 101 and in which a internal division ratio oftiming difference can be variably set such as in a programmable manner.

[0168] Referring to FIG. 12, in this interpolator, a P-channel MOStransistor MP1 has a source and a drain connected respectively to thepower source Vcc and to a internal node N31, respectively, and having agate fed with an output signal of a NAND circuit NAND 01 that receives afirst and second input signals IN1, IN2.

[0169] A inverter circuit INV3 of which input terminal is connected tothe internal node N31, switches a logical value of an output signal whenrelation of magnitude of the internal node potential and a thresholdpotential value of the inverter circuit INV3 are changed.

[0170] Inverter circuits INV1, INV2 have input terminals connectedrespectively to the first and second input signals IN1, IN2.

[0171] 16 N-channel MOS transistors MN11 ₁ to MN11 ₁₆ have drainsconnected in common to the internal node N31 and have gates connected incommon to an output of the inverter circuit INV1.

[0172] 16 N-channel MOS transistors (switching devices) MN12 ₁ to MN12₁₆ have drains connected in common to the internal node N31 and gatesconnected in common to an output of the inverter circuit INV2. 16N-channel MOS transistors MN21 ₁ to MN21 ₁₆ (switching devices) havedrains connected to the sources of N-channel MOS transistors MN11 ₁ toMN11 ₁₆ and sources connected to the constant current source I₀ andhaving gates connected to an output of an inverter circuit INV4 thatreceives and inverts a selection signal PH of a control circuit, such asa control circuit 102 of FIG. 1. 16 N-channel MOS transistors MN21 ₁ toMN21 ₁₆ are switched on or off on by a selection signal PH.

[0173] 16 N-channel MOS transistors MN22 ₁ to MN22 ₁₆ (switchingdevices) have drains connected to the sources of N-channel MOStransistors MN12 ₁ to MN12 ₁₆ and have sources connected to the constantcurrent source I₀, respectively, and having gates connected to andswitched on or off by a selection signal PH of a control circuit, suchas a control circuit 102 of FIG. 1.

[0174] A capacitance C is connected across the internal node N31 and theground GND.

[0175] The operation of the internal division in which N (N being 0 to16, with N=0 denoting no transistor being turned on and N beingdetermined by the control signal PH) of 16 parallel N-channel MOStransistors arc turned on with the input signal IN1, and in which (16−N)parallel N-channel MOS transistors are turned on after time T with theinput signal IN2, with the sum total of N+(16−N)=16 N-channel MOStransistors being turned on the whole, is hereinafter explained.

[0176] Current flowing through one of parallel N-channel MOS transistorsis I which is equal to a current value of the constant current sourceI₀.

[0177] With a threshold voltage V for switching an output of theinverter INV3, an amount of electrical charge required for reaching tothe threshold voltage is assumed to be CV.

[0178] It is assumed that the input signals IN1, IN2 are both at Highlevel, an output of the NAND 01 is at Low level and the internal nodeN31 has been charged from the power source through the P-channel MOStransistor MP1. It is also assumed that, in this state, the inputsignals IN1, IN2 fall to the Low level.

[0179] First, with N=16, 16 of the 16 N-channel MOS transistors MN11 ₁to MN11 ₁₆ are turned on. After time T, 16 parallel N-channel MOStransistors MN12 ₁ to MN12 ₁₆ are turned off by the input signal IN2((16−N) =0)). As a result, if N=16, the time T (16) until the output ofthe inverter INV3 is inverted after the input signal IN1 goes low is

T(16)CV/(16·1)  (3).

[0180] With N=n (n<16), where N is set by the control signal PH, nN-channel MOS transistors, the gates of which are fed with an invertedsignal of the input signal IN1, are turned on during the time T sincethe input signal IN1 falls at Low level, with T being the timingdifference between the input signals IN1 and IN2, so that n·I·T chargesare discharged.

[0181] The input signal IN2 falls at Low level, so that 16−n N-channelMOS transistors, the gates of which are fed with inverted signals of theinput signal IN2, are turned on. Thus, a sum total of the 16 N-channelMOS transistors are turned on.

[0182] At a time point T′ when electrical charges left in the internalnode N31 (CV−n·I·T) are discharged at (16·I), an output of the inverterINV3 is inverted, that is, goes from the High level to the Low level).The time T′ is given by

[0183] (CV−n·I·T)/(16·I).

[0184] So, time T(n) which elapses since the input signal IN1 falls atLow level until the output of the inverter INV3 is inverted is given by

T(n)=(CV−n·I·T)/(16·I)+T/(16·I)+T

=CV/(16·I)−(n/T)T+T

=T(16)+(16−n)/16)·T  (4).

[0185] By a value of n, output signal resulting having a phase that is16 equal division of timing difference T between the input signals IN1,IN2 are obtained. That is, by setting the control signal to vary n, anoutput signal with arbitrarily phase that is divided on a resolution{fraction (1/16)} of the timing difference between the input signalsIN1, IN2 are obtained. This interpolator is termed 16-step interpolator.

[0186] In general, if an interpolator is to be an M step interpolator,where M is an optional positive integer, M sets of N-channel MOStransistors MN11, MN12, MN13 and MN14 are arrayed in parallel.

[0187] The input IN1, IN2 of these interpolators arc fed with twosignals with a timing difference of e.g., 1 clock period tCK, and timingdifferences 0, tCK/16, 2tCK/16, . . . are output from the input IN1 eachinput clock to generate signals of clock period equal to tCK(1+{fraction (1/16)}).

[0188]FIG. 13 illustrates a circuit structure of an interpolator formingthe phase adjustment circuit 101 of FIG. 1. Referring to FIG. 13, inthis interpolator, a plurality of series circuits connected in parallelacross the internal node N31 and the ground are added to the circuitstructure shown in FIG. 12. Each of the series circuits is comprised ofN-channel MOS transistor switches and capacitors. Specifically, theseserial circuits are made up of switching devices MN21 to MN35 andcapacitors CAP11 to CAP 15. The capacitance attached to the internalnode is determined by the control signals connected to the controlterminals of switching devices MN11 to MN15. The capacitors CAP11 toCAP15 are of capacitance values C, 2C, 4C, 8C and 16C, with thecapacitance values added to the internal node being variably determinedby the values of the periodic control signal 7 of the switching devicesMN11 to MN 15. The periodic control signal 7 are set from outside andmay, for example, be a control signal 7 supplied from the perioddetection circuit 6 shown for example in FIG. 5.

[0189] In the interpolator shown in FIG. 12, the input node N31 ischarged to the power source potential when both the input signals IN1,IN2 are at High level, with the internal node N31 being dischargedresponsive to decay transition of the input signals IN1, IN2 from theHigh level to the Low level, with the output signal then rising from Lowlevel to High level. Alternatively, the output signal may rise from Lowlevel to High level responsive to a rise transition from Low level toHigh level of the input signal. For realizing the logic of the outputsignal going low from high responsive to the fall transition from Highlevel to Low level of the input signals IN1, IN2, it is sufficient ifthe inverter INV3 as a reversal buffer is designed as a non-invertingbuffer circuit.

[0190]FIG. 14 illustrates an alternative circuit structure of aninterpolator forming the phase adjustment circuit 101 shown in FIG. 1.Referring to FIG. 14, the interpolator comprises

[0191] a P-channel MOS transistor MP1, having a source and a drainconnected to a power source and to the internal node N31, respectively,and having a gate fed with an output signal of a NOR circuit NOR 01 fedin turn with the first and second input signals IN1, IN2, and aninverter circuit INV3 for switching the logical value of an outputsignal when the relative magnitude of the internal node potential andthe threshold potential value is changed.

[0192] The interpolator also includes 16N-channel MOS transistors MN11 ₁to MN11 ₁₆ having drains and gates connected in common to the internalnode N31 and to the input signal IN1, respectively, and

[0193] 16N-channel MOS transistors (switching devices) MN12 ₁ to MN12 ₁₆having drains and gates connected in common to the internal node N31 andto the input signal IN2, respectively.

[0194] The interpolator also includes 16N-channel MOS transistors MN21 ₁to MN21 ₁₆ (switching devices) having drains and sources connected tothe sources of N-channel MOS transistors MN11 ₁ to MN11 ₁₆ and to theconstant current source I₀, respectively, and having gates connected toan output of an inverter circuit INV4 and turned on or off. The invertercircuit INV4 is fed with a selection signal PH of a control circuit,such as a control circuit 102 of FIG. 1.

[0195] In addition, the interpolator includes 16N-channel MOStransistors MN22 ₁ to MN22 ₁₆ (switching devices) having drains andsources connected to the sources of N-channel MOS transistors MN12 ₁ toMN12 ₁₆ and to the constant current source I₀, respectively, and havinggates connected to and turned on or off by a selection signal PH of acontrol circuit, such as a control circuit 102 of FIG. 1.

[0196]FIG. 15 illustrates a structure in which a plurality of seriescircuits, each comprised of N-channel MOS transistor switches andcapacitors, and being connected in parallel across the internal node N31and the ground are added to the circuit structure shown in FIG. 14.Specifically, these serial circuits are made up of switching devicesMN21 to MN35 and capacitors CAP11 to CAP 15. The capacitance attached tothe internal node is determined by the control signals connected to thecontrol terminals of switching devices MN11 to MN15. The capacitorsCAP11 to CAP15 are of capacitance values C, 2C, 4C, 8C and 16C, with thecapacitance values added to the internal node being variably determinedby the values of the periodic control signal 7 of the switching devicesMN11 to MN15. The periodic control signal 7 is set from outside and may,for example, be the control signal 7 supplied from the period detectioncircuit 6 shown for example in FIG. 5.

[0197] In circuit configurations of the interpolators shown in FIGS. 12to 15, locations of transistors MN12, to MN12 ₁₆ and transistors MN22 ₁to MN22 ₁₆ may be interchanged and locations of transistors MN11 ₁ toMN11 ₁₆ and transistors MN21 ₁ to MN21 ₆ may be interchanged. Forexample, the interpolators shown in FIGS. 12 to 15 may be preferablyconfigured in such a structure wherein drains of the transistors MN22 ₁to MN22 ₁₆ of which gates are connected in common to the selectionsignal PH are connected to the node N31, and drains of the transistorsMN12 ₁ to MN12 ₁₆ of which gates are connected to the input terminal IN2are connected respectively to sources of the transistors MN22 ₁ to MN22₁₆ while sources of the transistors MN12 ₁ to MN12 ₁₆ are connectedrespectively to corresponding current sources I0, and wherein drains ofthe transistors MN21 ₁ to MN21 ₁₆ of which gates are connected in commonto the output of the inverter INV4 are connected to the node N31, anddrains of the transistors MN11 ₁ to MN11 ₁₆ of which gates are connectedto the input terminal IN1 are connected respectively to sources of thetransistors MN21 ₁ to MN21 ₁₆, while sources of the transistors MN11 ₁to MN11 ₁₆ are connected respectively to corresponding current sourcesI0.

[0198] A further embodiment of the present invention is explained. FIG.16 shows a structure of a fourth embodiment of the present invention,according to which, in the clock control circuit comprised of thefrequency divider 103, phase adjustment circuit 101 and the controlcircuit 102, shown in FIG. 3, the phase adjustment circuit 101 is formedby an interpolator shown in FIGS. 12 to 15.

[0199] The interpolator 110 receives a first and second input signalsIN1, In2. The first input signal IN1 is a clock signal supplied from afirst D-flipflop 113 that latches with a clock fed to a clock terminalthereof, a signal which is a frequency-divided clock from a frequencydivider 103 that received a clock and is fed to a data input terminalthereof and the second input signal IN2 is a clock signal supplied froma second D-flipflop 114 that latches with a clock fed to a clockterminal thereof, an output signal from the D-flipflop 113.

[0200] The interpolator 110 divides timing difference of the first andsecond input signals IN1, IN2 (period tCK of the clocks CLK) with aninternal division ratio as set by a control signal (selection signal)output by a control circuit 102 which comprises an adder 112 thatreceives the clock and a decoder 111 that decodes an output or the adder112.

[0201]FIG. 17 illustrates a timing waveform diagram for illustrating anexemplary operation of the circuit shown in FIG. 16. The frequencydivider 103 frequency divides the clock. The interpolator 110 iscomprised of the circuit shown in FIG. 14. When the input signals IN1,IN2 are both at Low level, the internal node of the interpolator 110 ischarged. When the input signals IN1, IN2 rise from Low level to Highlevel, the internal node N31 is discharged, such that an output signalOUT, rising at a timing corresponding to division of the timingdifference of the input signals IN1, IN2 (clock period tCK) with theinternal dividing ratio as set by the control signal PH, is output viaan inverter circuit INV3.

[0202] Referring to FIG. 17, the signal OUT from the interpolator 110rises from Low level to High level, with a delay ΔΦ as from rising edgeof the clock at clock cycle T2.

[0203] At clock cycle T4, the input signals IN1, IN2 fed to theinterpolator both are at Low level, with the internal node N31 beingcharged to the power source potential, with the output OUT being at Lowlevel. The value of the control signal PH supplied to the gates of theN-channel MOS transistors MN21 and MN22 is switched, with the signal OUTfrom the interpolator I0 rising from Low level to High level after delayof time 2ΔΦ from rising edge of the clocks of the clock cycle T6. Inthis case, the period of the output clock from the interpolator 110 is4tCK+ΔΦ.

[0204] By varying the setting value of the control signal (selectionsignal of FIG. 1) supplied to the N-channel MOS transistors MN21 andMN22 of the interpolator 110 (see FIGS. 12 to 15) at preset timing inone clock cycle of the frequency divided clock, the timing of the outputclock relative to the edge of the input clock (phase difference) may bechanged to convert the frequency.

[0205] Another embodiment of the present invention is hereinafterexplained. FIG. 18 illustrates a structure of a fifth embodiment of thepresent invention in which an interpolator shown in FIGS. 12 to 15 isused in the phase adjustment circuit 101 shown in FIG. 1. Referring toFIG. 18, the present embodiment includes D-flipflops 211, 212, two-stageserial circuits, in which an output of an inverter INV that receives anoutput signal of the back stage D-flipflops 212 is fed back to a dataterminal D of the frond stage D-flipflops 211, and first to fourthD-flipflops 213 to 216, connected in a cascade to form a shift register,fed with an output of the D-flipflop 212 as an input.

[0206] The present fifth embodiment also includes a first interpolator217, fed with outputs Q1, Q2 of the first and second flipflops 213, 214as inputs and outputting a signal of the time delay corresponding to thedivision of the timing difference T, a second interpolator 218, fed withoutputs Q2, Q3 of the second and third flipflops 214, 215 as inputs andoutputting a signal of the time delay corresponding to the division ofthe timing difference T, a third interpolator 219, fed with outputs Q3,Q4 of the third and fourth flipflops 215, 216 as inputs and outputting asignal of the time delay corresponding to the division of the timingdifference T, and a fourth interpolator 219, fed with outputs Q4, Q1 ofthe fourth and first flipflops 216, 213 as inputs and outputting asignal of the time delay corresponding to the division of the timingdifference T. The first to fourth interpolators 217 to 220 are fed witha control signal 222, setting the internal division ratio of the timingdifference, from a control circuit, not shown.

[0207] The value of the control signal 222 supplied to the first tofourth interpolators 217 to 220 may be fixed without being changed onthe clock basis.

[0208]FIG. 19 illustrates a typical operation of the circuit shown inFIG. 18 Referring to FIG. 19, the first interpolator 217 outputs anoutput signal obtained on division of the timing difference tCK of thesignals Q1, Q2 (with a timing difference ΔΦ from the rising edge of theclock of the clock cycle T2). The second interpolator 218 outputs anoutput signal obtained on division of the timing difference tCK of thesignals Q2, Q3 (with a timing difference 2ΔΦ from the rising edge of theclock of the clock cycle T2). The third interpolator 219 outputs anoutput signal obtained on division of the timing difference tCK of thesignals Q3, Q4 (with it timing difference 3ΔΦ from the rising edge ofthe clock of the clock cycle T4). The fourth interpolator 220 outputs anoutput signal obtained on division of the timing difference tCK of thesignals Q4, Q1 (with a timing difference 4ΔΦ from the rising edge of theclock of the clock cycle T2=beginning of the clock period tCK). In thiscase, the interpolator outputs clocks with a period of tCK(1+¼) for aninput clock (clock period tCK).

[0209] The first to fourth interpolators 217 to 220 may output theresults calculated by a logic circuit depending on the application, orselectively output the result via a selector. The present invention maybe applied with advantage to a rate conversion circuit in e.g., mBnB (mbits n bits) coding system.

[0210] A further embodiment of the present invention is hereinafterexplained. FIG. 20 illustrates a structure of a sixth embodiment of thepresent invention. Referring to FIG. 20, the present embodiment includesan interpolator for frequency-multiplication 10, a switch (rotaryswitch) 20, an interpolator 30, also called a fine adjustmentinterpolator, and a control circuit 40.

[0211] The interpolator for frequency-multiplication 10 generatesmultiple-phase frequency-multiplication clocks P0 to Pn from the inputclock 1.

[0212] The interpolator for frequency-multiplication 10 is configured asshown in FIG. 5.

[0213] The switch 20 selects two of the clocks from the multiple-phasefrequency-multiplication clocks P0 to Pn to furnish the selected clocksas two input signals to the fine adjustment interpolator 30.

[0214] The control circuit 40 furnishes control signals S for the switch20 and the fine adjustment interpolator 30 and the PH (control signalfurnished to the gates of the N-channel MOS transistors 21, 22 of theinterpolator 30). The control circuit 40 includes an adder, not shown,fed with clocks 1, and a decoder, not shown, for decoding an output ofthe adder to output the control signals D and the PH.

[0215] The switch 20 selects odd-phased signal and even-phased signal,neighboring to each other, based on the control signal S from thecontrol circuit 40 to furnish the selected clock pair to theinterpolator 30, which then outputs, based on the control signal fromthe control circuit 40, a signal of the phase corresponding to theinternal division of the phase difference (timing difference) of the twoinputs. In the present embodiment, the interpolator 30 is configured asshown in FIGS. 12 to 15.

[0216]FIG. 21 Illustrates a typical operation for a case wherein theinterpolator 30 is constructed by a circuit shown in FIG. 15 and whereinthe interpolator for multiplication 10 (see FIG. 5) generates four-phasemultiplication clocks P0 to P3.

[0217] The rotary switch 20 cyclically selects multi-phase clocks, fromthe multi-phase clocks P0 to P3, in the order of, for example, (P0, P1),(P1, P2), (P2, P3), (P3, P0), (P0, P1), . . . With the period of themulti-phase clocks T, the switch 20 selects P0, P1 at a clock cycle T1,whilst the interpolator 30 is responsive to the rising of P0, P1 toissue an output signal OUT. At a cycle T2, the switch 20 selects P1, P2,while the interpolator 30 is responsive to the rising of P1 and P2 tooutput an output signal OUT at a timing of time (1+¼) as from the risingedge of the previous output signal OUT. In similar manner, the switchselects P3 and P4, followed by P4, P1, to output clocks with the periodT (1+¼).

[0218] In the embodiment shown in FIG. 21, the interpolator isoutputting clocks with a period (1+¼)T 5T/4 for the period T of themultiplication clocks, with the frequency being ⅘ times that of theclock period. If the interpolator for multiplication 10 is multiplyingthe input clock by a factor of 2m, the frequency of the output clocks ismultiplied by a factor of 8m/5.

[0219] A further embodiment of the present invention is hereinafterexplained. FIG. 22 shows the structure of a seventh embodiment of thepresent invention. Referring to FIG. 22, the seventh embodiment of thepresent invention is a modification of the structure shown in FIG. 20.That is, a rotary switch 20 outputs two sets of paired clocks which arefed to first and second interpolators 30 ₁, 30 ₂, outputs of which arefed to a third interpolator 10 ₃ as inputs. Output clocks are obtainedfrom an output of the third interpolator 10 ₃.

[0220] In the present embodiment, the ratio of the internal division ofthe timing difference of the respective interpolators of the first tothird interpolators 30 ₁ to 30 ₃. Alternatively, responsive to thetiming accuracy as found by the application, the ratio of internaldivision of the timing difference of the interpolator 30 ₁ may be fixedwhile that of the interpolators 30 ₂, 30 ₃ may be varied by the controlsignals from the control circuit 40. Still alternatively, the ratio ofthe internal division of the interpolators 30 ₂, 30 ₃ may be varieddepending on the control signal from the control circuit 40. The ratioof the internal division of the timing difference of the interpolators30 ₁, 30 ₂ may be fixed, while that of only the last stage interpolator30 ₁ may be varied with the control signal from the control circuit 40.

[0221] In a seventh embodiment of the present invention, the fineadjustment interpolators 30 are arranged in a multi-stage configuration,in distinction from the structure shown in FIG. 20, whereby the ratio ofthe internal division of the timing difference may be set to a finervalue. In case the second and third interpolators 30 ₂, 30 ₃ arearranged as 16 equi-divisional interpolators, the timing difference maybe internally divided to a resolution of {fraction (1/256)}.

[0222] An eighth embodiment of the present invention is hereinafterexplained. In FIG. 23, showing a modification of the configuration shownin FIG. 3, clocks are frequency divided by a frequency divider 60 tooutput two paired clocks which are furnished to the first and secondinterpolators 30 ₁, 30 ₂. Output clocks are derived from an output ofthe third interpolator 30 ₃, fed as input with the outputs of the twointerpolators 30 ₁, 30 ₂.

[0223] A ninth embodiment of the present invention is hereinafterexplained. Referring to FIG. 24, the ninth embodiment of the presentinvention is a modification of the embodiment shown in FIG. 18, andincludes an interpolator for frequency-multiplication 10 for generatingfirst to nth clocks P1 to Pn (n-phased multiplication clocks) ofrespectively different phases, obtained on multiplication of the inputclock, first to nth interpolators 30 ₁ to 30 _(n), and a synthesis unit50 fed with outputs of the first to nth interpolators 30 ₁ to 30 _(n)(fine adjustment interpolators) to multiplex the input signals to unifythe signals to output a sole output signal OUT. The first to nthinterpolators 30 ₁ to 30 _(n) are fed with two clocks of neighboringphases of the first to nth clocks P1 to Pn from the interpolator formultiplication 10 to output a signal corresponding to division byrespectively different ratios of internal division of the timingdifference of the two input signals.

[0224] The first to nth interpolators 30 ₁ to 30 _(n) are configured asshown in FIGS. 12 to 15 to divide the timing difference T of the twoinput signals by m steps, where n≦m. With the interpolator formultiplication 10 and fine adjustment interpolator 30 for generating then-phased multiplication clocks, it is possible to generate the timingcorresponding, to division by n×m steps as output signal OUT.

[0225] In the embodiment shown in FIG. 24, similarly to theconfiguration shown in FIG. 18, the interpolator 30 ₁ fed withneighboring ith and (i+1)st clocks of the n-phase clocks, as inputs,where i is an integer from 1 to n, with the (n+1)st clock being thefirst clock P1), and the interpolator 30 _(i−1) with the (i−1)st andPith clocks as inputs, are set so that the values of the ratio of theinternal division of the timing difference thereof will differ from eachother. Specifically, the delay time of the interpolator 30 ₁ is largerthan that of the interpolator 30 _(i−1).

[0226] The synthesis unit 50 for multiplexing outputs of the first tonth interpolators 30 ₁ to 30 _(n) for outputting an output signal OUT ismade up of a pulse width correction circuit 4 c and a multiplicationcircuit 4 b.

[0227] In the configuration of FIG. 24, the configuration of generatingM-phase clocks (M multiplication clocks) from the n-phase multiplicationclocks, output from the interpolator for multiplication 10, isexplained. In this case, M interpolators are arranged in parallel, whereM≦N.

[0228] In this case, the ith interpolator 30 ₁ is fed with neighboringith and (i+1)st clocks, where i is an integer from 1 to M and the(n+1)st clock is the first clock P1. The values of the ratio of theinternal division prescribing the division positions of the timingdifference between the two input signals in the respective interpolators30 are set as the values are sequentially shifted from the leading endtowards the trailing end of the timing domain, each unit step m, in theincreasing sequence of the interpolator numbers, such as,

[0229] for the 1st interpolator 30 ₁, the internal division ratio m;M-m, for the 2nd interpolator 30 ₁, the internal division ratio 2m;M-2m,for the 3rd interpolator 30 ₃, the internal division ratio 3m;M-3m.

[0230] Alternatively, the division positions of the timing difference Tmay be set as the values are sequentially shifted from the trailing endtowards the leading end of the timing domain, each unit step m, in theincreasing sequence of the interpolator numbers.

[0231] This setting may be achieved by controlling the on/off of theN-channel MOS transistors MN21 and MN22, with the control signal PHsupplied to the interpolator, as explained with reference to FIGS. 12 to15. In the present embodiment, the value of the ratio of the internaldivision of each interpolator is fixed.

[0232] From the synthesis unit 50, multiplexing the outputs of the minterpolators 30 to a sole output signal OUT, M-tupled clocks may beproduced. For example, with m=1 for n=8 and M=7, seven-phased clocks maybe generated from the eight-phase clocks (eight-phased clocks) Outputfrom the interpolator for multiplication 10. From the synthesis unit 50,fed with the seven-phased clocks, 7-tupled(multiplied by 7 in frequency)clock is output.

[0233]FIG. 25 illustrates an example of a layout of an integratedcircuit of a 16-equi-division interpolator.

[0234]FIG. 26 shows waveforms obtained by a circuit simulation of aphase adjustment circuit employing a fine adjustment interpolator. Phasedifference of 625 MHZ is divided into 16 equal portions by a16-equal-dividing interpolator and five phases of the phase changeoverportion are shown. The fine adjustment phase difference is 12.5 ps.

[0235] In the above-described embodiment of the present invention, inwhich the interpolators are arrayed in plural stages, the timing edge ofan output signal can be controlled to an order of 10 psec. That is, thepresent invention is applicable not only to a clock frequency conversioncircuit or a clock synchronization circuit but also to a patterngenerator or a timing generator in a measurement and testing device. Forexample, the present invention may be used with advantage in a timinggenerator for an LSI tester in which the timing is variably seton-the-fly.

[0236] The configuration having a frequency divider and a phaseadjustment circuit (interpolator for phase adjustment) as explained withreference to FIGS. 3 and 23, for example, may be applied to a frequencydivider in a PLL (phase locked loop) having a charge pump for generatingthe voltage corresponding to the phase difference of the phasecomparator, a loop filter, a VCO (voltage-controlled oscillator) fedwith an output of the loop filter as a control voltage and a frequencydividing circuit for supplying a signal obtained on frequency divisionof the VCO output to the phase comparator.

[0237] The meritorious effects of the present invention are summarizedas follows. According to the present invention, as described above,non-integer frequency conversion may be achieved to high precisiondespite a simpler structure.

[0238] The reason is that such a configuration is used in the presentinvention in which the phases of the signals output from the phaseadjustment circuit fed with clocks as inputs may be summed or subtractedby unit phase difference on the clock basis.

[0239] According to the present invention, there is provided on feedbacksystem, not jitter proper to the feedback system, thus enablinghigh-speed clock synchronization. It should be noted that other objects,features and aspects of the present invention will become apparent inthe entire disclosure and that modifications may be done withoutdeparting the gist and scope of the present invention as disclosedherein and claimed as appended herewith.

[0240] Also it should be noted that any combination of the disclosedand/or claimed elements, matters and/or items may fall under themodifications aforementioned.

What is claimed is:
 1. A clock control circuit comprising: means forgenerating and outputting an output clock having a phase relative to areference clock by adding or subtracting to or from said phase by apredetermined unit value of a phase differential on each clock period ofsaid reference clock, said reference clock being an input clock or aclock derived from the input clock.
 2. A clock control circuitcomprising: control means for producing a control signal for adding orsubtracting to or from a phase relative to a reference clock, by apredetermined unit value of a phase differential, on each clock periodor said reference clock, said reference clock being an input clock or aclock generated from the input clock; and phase adjustment means fedwith the input clock for generating an output clock having a phaserelative to said reference clock, said phase being added or subtractedby the predetermined unit value of the phase differential based on saidcontrol signal; whereby said output clock of a frequency is allowed tobe in a non-integer relation with respect to a frequency of saidreference clock.
 3. A clock control circuit comprising: a controlcircuit for generation of a control signal for adding or subtracting toor from a phase difference of an output clock relative to an input clockby a unit value of a phase difference; and a phase adjustment circuitfed with said input clock for generating and outputting an output clockhaving said phase difference prescribed by said control signal.
 4. Aclock control circuit comprising: a frequency dividing circuit fed withan input signal to frequency divide the input clock to output anfrequency divided clock; a control circuit for generation of a controlsignal adding or subtracting to or from a phase difference relative tosaid frequency divided clock by a unit value of a phase difference basedon the frequency divided clock output from said frequency dividingcircuit; and a phase adjustment circuit fed with said input clock andgenerating and outputting an output clock having said phase prescribedby said control signal from said control circuit.
 5. A clock controlcircuit comprising: a multi-phase clock generating circuit forgenerating and outputting first to nth clocks having respectivedifference phases from an input clock received; a selector fed with saidfirst to nth clocks to select and output one of said first to nthclocks; and a control circuit fed with an input clock to generate aselection signal for selecting sequentially said first to nth clocks toprovide the generated selection signal to said selector.
 6. The clockcontrol circuit as defined in claim 4 wherein said unit value of thephase difference is variably set by a mode signal input from outside. 7.The clock control circuit as defined in claim 5 wherein an output of theselection signal controlling selection of said selector is variably setby a mode signal input to said control circuit.
 8. A clock controlcircuit comprising: a multi-phase multiplication clock generatingcircuit receiving an input clock to generate first to nth clocks ofrespective different phases (termed, multi-phase multiplication clocks)obtained by frequency multiplying said input clock; a switch forselecting two clock signals of said first to nth clocks output from saidmulti-phase multiplication clock generating circuit; at least oneinterpolator receiving the two clock signals selected and output by saidswitch to generate an output signal, a propagation delay of said outputsignal corresponding to division of timing difference of said two clocksignals, with a ratio of a internal division being variably set; and acontrol circuit for producing a switching signal for said switch and acontrol signal for variably setting a ratio of internal division of thetiming difference of said interpolator.
 9. A clock control circuitcomprising: a multi-phase multiplication clock generating circuitreceiving an input clock to generate first to nth clocks of respectivedifferent phases (termed multi-phase multiplication clocks) obtained byfrequency multiplying the input clock; a switch for selecting two setseach of two neighboring ones of said first to nth clocks output fromsaid multi-phase multiplication clock generating circuit; a firstinterpolator receiving the first set of two clocks output from saidswitch to generate a first signal, a propagation delay of said firstsignal corresponding to division of timing difference of said two clocksignals; a second interpolator receiving the second set of two clocksoutput from said switch to generate a second signal, a propagation delayof said second signal corresponding to division of timing difference ofsaid two clock signals; a third interpolator receiving said first andsecond signals of said first and second interpolators to generate athird signal, a propagation delay of said third signal corresponding todivision of timing difference of said first and second signals; a ratioof the internal division of the timing difference of at least one ofsaid first to third interpolators being variably set; and a controlcircuit for outputting a switching signal for said switch and a controlsignal for variably setting the ratio of the internal division of thetiming difference of said interpolators.
 10. A clock control circuitcomprising: a frequency divider receiving an input clock to generate twosets of clocks of respective different phases obtained on frequencydivision or said input clock; a first interpolator receiving the firstset of two clocks output from said frequency divider to generate a firstsignal, a propagation delay of said first signal corresponding todivision of timing difference of said two clock signals; a secondinterpolator receiving the second set of two clocks output from saidfrequency divider to generate a second signal, a propagation delay ofsaid second signal corresponding to division of timing difference ofsaid two clock signals; a third interpolator receiving outputs of saidfirst and second interpolators to generate a third signal, a propagationdelay of third signal corresponding to division of timing difference ofsaid two outputs; a ratio of internal division of the timing differenceof at least one of said first to third interpolators being variably set;and a control circuit for outputting a switching signal for said switchand a control signal for variably setting the ratio of internal divisionof the timing difference of said interpolators.
 11. A clock controlcircuit comprising: a multi-phase multiplication clock generatingcircuit receiving an input clock to generate a plurality of clocks ofrespective different phases (termed multi-phase multiplication clocks)obtained on multiplying the input clock; a plurality of interpolatorsreceiving respectively two clocks of neighboring phases of said pluralclock outputs from said multi-phase multiplication clock generatingcircuit to output signals corresponding to division with respectivedifferent values of the ratio of internal division of the timingdifference of said two clocks; and a synthesis unit fed with outputs ofsaid plural interpolators to multiplex said outputs from said pluralityof interpolators to output as resulting sole output signal.
 12. Theclock control circuit as defined in claim 11 wherein said multi-phasemultiplication clock generating circuit generates N phase clocks, whereN is a preset positive integer, M of said interpolators are provided,where M is a positive integer, such that M ≦N, an ith one of saidinterpolators is fed with ith and (i+1)st clocks, where i is an integerfrom 1 to M, with the (n+1)st clock being a first clock; a value of aratio of the internal division dividing the timing difference of twoinput signals in each of said interpolator being so set that a ratiovalue of the (i+1)st interpolator is larger or smaller than that of theith interpolator by a preset unit step; M-phase clocks being output fromsaid M interpolators; and wherein an output clock of a multiplied by Mfrequency is output from said synthesis unit.
 13. The clock controlcircuit as defined in claim 5 wherein said multi-phase clock generatingcircuit comprises a multi-phase multiplication clock circuit forfrequency dividing said input clock to generate multi-phase clocks togenerate a signal by frequency multiplying, said multi-phase clocks. 14.A clock control circuit as defined in claim 8 wherein said multi-phasemultiplication clock generating circuit comprises a frequency dividingcircuit for frequency dividing input clock to generate and output aplurality of clocks of different phases (multi-phase clocks); a perioddetection circuit for detecting the period of said input clock; and amulti-phase clock multiplication circuit fed with the multi-phase clocksform a frequency dividing circuit to generate multi-phase clockscorresponding to multiplication of said clocks; said multi-phase clockmultiplication circuit comprising: a plurality of timing differencedivision circuits for outputting a signal corresponding to division oftiming difference of two inputs; and a plurality of multiplexingcircuits multiplexing two outputs of said timing difference divisioncircuits to output the resulting multiplexed signals; said timingdifference division circuits comprising a timing difference divisioncircuit fed with clocks of the same phase and a timing differencedivision circuit fed with two clocks of neighboring phases.
 15. Theclock control circuit as defined in claim 14 wherein said multi-phaseclock multiplication circuit is fed with n-phase clocks (first to nthclocks); there being provided 2n timing difference division circuits foroutputting signals corresponding to division of the timing difference oftwo inputs; a (2I-1)st timing difference division circuit, where 1≦I≦n,is fed with the same Ith clocks as said two inputs; a 2Ith timingdifference division circuit, where 1≦I≦n, being fed with the Ith clockand with the (I+1 mod n)th clock, where mod denotes a remainderoperation and I+1 mod n indicates a remainder of a division of (I+1) bym; there being provided 2n pulse width correction circuits fed with anoutput of a Jth timing difference division circuit, where 1≦J≦2n, andwith an output of a (J+2 mod n)th timing difference division circuit,where J+2 mod n means the remainder of division of J+2 with n; therebeing also provided n multiplexing circuits fed with an output of a Kthpulse width correction circuit, where 1≦K≦n, and with an output of the(K+n)th pulse width correction circuit.
 16. The clock control circuit asdefined in claim 14 wherein said timing difference division circuitincludes a NOR circuit receiving first and second input signals; and aninverter receiving a voltage level of an internal node that is an outputof said NOR circuit; a plurality of series circuits each made up of aswitching device and a capacitance device are connected in parallelacross said internal node and the ground; capacitance to be attached tosaid internal node being determined by a period control signal coupledto a control terminal of said switch.
 17. The clock control circuit asdefined in claim 14 wherein said timing difference division circuitincludes a logic circuit receiving first and second input signals andoutputting a result of a preset logical operation on said first andsecond input signals; a first switching device connected across a firstpower source and an internal node and having an output signal of saidlogic circuit fed as input to a control terminal thereof; a buffercircuit an input terminal of which is connected to said internal nodeand an output logical value of which is changed on inversion of relativemagnitudes of said internal node potential and a threshold value; afirst constant current source connected in series across said internalnode and a second switch device and a second switch device controlled onor off by said first input signal; and a second constant current sourceconnected in series across said internal node and the second powersource and a third switching device controlled on or off by said secondinput signal; a plurality of series circuits each made up of a fourthswitching device and a capacitance device are connected in parallelacross said internal node and said second power source; capacitance tobe attached to said internal nod being determined by a period controlsignal coupled to a control terminal of said fourth switching device.18. The clock control circuit as defined in claim 17 wherein said firstswitch device is a MOS transistor of a first conductivity type; saidsecond to fourth switch devices being MOS transistors of a secondconductivity type.
 19. A clock control circuit comprising: aninterpolator receiving a frequency divided signal produced by afrequency dividing circuit receiving a clock signal and a signalobtained by shifting the frequency divided signal in a preset number ofperiods of the clock to produce a signal obtained on division of atiming difference of said two input signals at a preset ratio ofinternal division; and a control circuit for varying value of the ratioof the internal division of the timing difference in said interpolatorbased on said clock signals.
 20. A clock control circuit comprising: aplurality of (N) interpolators for outputting signals obtained ondividing a timing difference of two input signals with respectivedifferent values of a preset ratio of internal division; wherein offirst to nth clocks with respective different phases, two clocks, thatis the Ith and the (I+1)st clocks, where I is an integer from 1 to N,with N+1 being 1, are input to the Ith interpolator.
 21. The clockcontrol circuit as defined in claim 8 wherein said interpolatorcomprises a logic circuit fed with first and second input signals tooutput results of preset logical processing of said first and secondinput signals; a first switching device connected across a first powersource and an internal node, said first switching device being fed at acontrol terminal thereof with an output signal of said logic circuit andbeing turned on when said first and second input signals are both of afirst value; a buffer circuit having an input terminal connected to saidinternal node and having an output logical value changed on inversion ofthe relative magnitudes of the terminal voltage of the capacitance ofsaid internal node and a threshold value; a plurality of serial circuitsconnected across said internal node and a second power source inparallel, each of said serial circuits being made up of a secondswitching device turned on when said first input signal is of a secondvalue, said third switch device turned on or off based on a controlsignal from said control circuit, and a first constant current source;and a plurality of serial circuits connected across said internal nodeand a second power source in parallel, each of said serial circuitsbeing made up of a fourth switching device turned on in common when saidfirst input signal is of a second value, said fifth switching deviceturned on or off based on a control signal from said control circuit,and a constant current source.
 22. The clock control circuit as definedin claim 8 wherein said interpolator comprises: a logic circuitreceiving first and second input signals to output a result of presetlogical processing of said first and second input signals; a firstswitching device connected across a first power source and an internalnode, said first switching device being fed at a control terminalthereof with an output signal of said logic circuit and being turned onwhen said first and second input signals are both of a first value; abuffer circuit having an input end connected to said internal node andhaving an output logical value changed on inversion of the relativemagnitudes of the terminal voltage of the capacitance of said internalnode and a threshold value; a plurality of serial circuits connectedacross said internal node and a second power source in parallel each ofsaid serial circuits being made up of a second switching device turnedon when said first input signal is of a second value, said third switchdevice turned on or off based on a control signal from said controlcircuit, and a first constant current source; a plurality of serialcircuits connected across said internal node and a second power sourcein parallel, each of said serial circuits being made up of a fourthswitching device turned on in common when said first input signal is ofa second value, said fifth switching device turned on or off based on acontrol signal from said control circuit, and a constant current source;and a plurality of serial circuits connected across said internal nodeand the second, power source in parallel, each said serial circuit beingmade up of a sixth switching device and a capacitor; wherein capacitancevalue attached to said internal node is determined by a period controlsignal supplied to a control terminal of said sixth switching device.23. The clock control circuit as defined in claim 21 wherein a pluralityof (N) of each of said second, third, fourth and fifth switching devicesare provided; K of said third switching devices are turned on by acontrol signal supplied to a group of said third switching devices,where K is 0 to N; (N-K) of said fifth switching devices are turned onby a control signal supplied to said group of said fifth switchingdevices; signals corresponding to the timings obtained on K-basedinternal division of the timing difference of said first and secondinput signals. in terms of a nth fraction of said timing difference as aunit, are output, with the value of said K being changed to vary theratio of the internal division of said timing difference.
 24. The clockcontrol circuit as defined in claim 23 wherein the control signalsupplied from said control circuit to a control terminal of said thirdswitching device is complemented by an inverter and supplied as acontrol signal to a control terminal of said fifth switching devicecorresponding to said third switching device.
 25. The clock controlcircuit as defined in claim 21 wherein said first switching device is aMOS transistor of a first conductivity type; and wherein said second tofifth switching devices are MOS transistors of a second conductivitytype.
 26. The clock control circuit as defined in claim 22 wherein saidfirst switching device is a MOS transistor of a first conductivity type;and wherein said second to sixth switching devices are MOS transistorsof a second conductivity type.
 27. The clock control circuit as definedin claim 22 wherein said period control signal is supplied from saidperiod detection circuit for detecting a period of the input clock. 28.A clock control method comprising the steps of: generating an outputclock having a phase relative to a reference clock by adding orsubtracting to or from said phase by a predetermined unit value of aphase differential on each clock period of said reference clock, saidreference clock being an input clock or a clock derived from the inputclock; and outputting said output clock.
 29. The clock control method asdefined in claim 28 wherein the output clock of a frequencycorresponding to a non-integer frequency with respect to the frequencyof said reference clock can be output.
 30. A clock control methodcomprising the steps of: frequency dividing an input clock by afrequency divider receiving the input clock; generating a controlsignal, based on the frequency divided clock, for adding or subtractingby a preset unit value of a phase differential to or from a phasedifference relative to the frequency divided clock; and generating anoutput clock of the phase difference as set by said control signal. 31.The clock control method as defined in claim 28 wherein the unit phasedifference is variably set by a control signal.
 32. A clock controlmethod comprising: generating first to Nth clocks of respectivedifferent phases (termed multi-phase clocks) from an input clock toprovide the generated clocks to a selector and wherein said selectorsequentially selects and outputs said first to Nth clocks.
 33. The clockcontrol method as defined in claim 28 wherein the output clock isphase-adjusted by an interpolator outputting a signal, a propagationdelay of said signal corresponding to division of timing difference oftwo clock signals to vary ratio of internal division of timingdifference of said interpolator to enable outputting of an output clockof a frequency which is an non-integer frequency of the input clockfrequency.
 34. A clock control circuit comprising: a circuit thatreceives an input clock and generates an output clock with a phaserelative to a reference clock being changed on each cycle of the outputclock, said reference clock being the input clock or a clock derivedfrom the input clock, wherein a phase of the output clock relative tothe reference clock for another cycle next to one cycle is produced byadding to the phase of the output clock corresponding to said one cyclea unit phase differential value ΔΦ, where the ΔΦ is a predeterminedvalue such that n ΔΦ is equal to one clock period (tCK) of saidreference clock while said n is an positive integer, and whereby afrequency of the output clock is 1/(tCK+ΔΦ).
 35. A clock control circuitcomprising: circuit that receives an input clock and generates an outputclock with a phase relative to a reference clock being changed on eachcycle of the output clock, said reference clock being the input clock ora clock derived from the input clock, wherein a phase of the outputclock relative to the reference clock for another cycle next to onecycle is produced by subtracting from the phase of the output clockcorresponding to said one cycle a unit phase differential value ΔΦ,where the ΔΦ is a predetermined value such that n ΔΦ is equal to oneclock period (tCK) of said reference clock while said n is an positiveinteger, and whereby a frequency of the output clock is 1/(tCK-ΔΦ). 36.A clock control circuit comprising: a control circuit unit comprising:an adding circuit that increments an output on receipt of an input clockpulse by a predetermined unit m, wherein the m is a positive integer andis variably set; and a decoder that decodes the output of the addingcircuit to generate a control signal; and a phase adjustment circuitthat receives the input signal and the control signal to generate anoutput clock wherein a phase of said output clock to a correspondingedge of the input clock is incremented by a unit phase differentialvalue mΔΦ, on each cycle of said input clock, where the ΔΦ is apredetermined value such that n ΔΦ is equal to one clock period (tCK) ofsaid input clock, said n being an positive integer, whereby a frequencyof said output clock is 1/(tCK+m ΔΦ).
 37. A clock control circuitcomprising as define in claim 36 comprising a circuit that receives theinput clock and generates first and second signals from the input clock,between edges of said first and second signals a preset timingdifference being provided, wherein said phase adjustment circuitcomprises an interpolator that receives said first and second signalsand generates the output signal having a propagation delay correspondingto a time of an internal division ratio of the timing difference betweensaid first and second signals, said internal division ratio beingchanged by said control signal on each cycle of one of said first orsecond signal.